Hi Cherries,
I've had the same difficulties in the past. I've been with a girlfriend, found her really attractive, but just not wanted to have sex with her.
The solution was exploration of fantasy. But this can be hard for some people. I highly recommend looking at a series of books by Nancy Friday, which have real male and female fantasies submitted by real people.... Its a great read! Why not read it to him??
Good luck!
Love one another, but make not a bond of love:
Let it rather be a moving sea between the shores of your souls.
Kahlil Gibran